Hydrocyclones for oil spill cleanup having a controlled split ratio

ABSTRACT

An oil spill recovery system includes a first hydrocyclone separator and optionally a second hydrocyclone separator located on a floating vessel floating on a body of water from which spilled oil is to be recovered. A recovered fluid containing oil and water emulsion and a large amount of free sea water is recovered from the body of water. The first hydrocyclone separator separates the recovered fluid into a first underflow stream containing oily water and a first overflow stream which contains substantially all of said oil and water emulsion. The oily water underflow stream from the first hydrocyclone separator is then directed to a second hydrocyclone separator which separates it into a second underflow stream which is returned to the sea as clean water, and a second overflow stream. The first overflow stream is stored in on-board ship&#39;s storage. The second overflow stream may be stored in ship&#39;s storage or recycled for further separation.

This is a division of application Ser. No. 07/971,901 filed Dec. 21,1992, now U.S. Pat. No. 5,366,641.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to processes and systems forseparating oil and water, and more particularly, to oil spill recoverysystems.

2. Description of the Prior Art

Commercial oil spill recovery skimmers can recover a fluid stream whichtypically comprises ten percent by volume oil and water emulsion andninety percent by volume unwanted free sea water. The oil and wateremulsion itself typically contains at least fifty percent, and perhapsas much as ninety percent, water. The condition of the recovered fluidvaries greatly depending on the thickness of the oil layer, the state ofthe seas, the time the spill has weathered, etc. In a typical oil spillrecovery vessel having no oil and water separation system located onsite all of the recovered fluid is stored in the vessel. Thus the storedfluid may contain up to ninety-nine percent by volume water. If the oiland water could be efficiently separated on site so that the water or alarge portion thereof could be returned to the sea and only therecovered oil stored, the oil spill recovery vessels' ability to remainon site and operate for long periods of time could be greatly extended.

The prior art does include systems which have been proposed for theon-site separation of oil and water from recovered oil spill fluids.

One system proposed by Jastram-Werke GmbH of Hamburg, Germany, known asthe ORAS system uses an oil/water separator made up of a system of weirsand gates.

U.S. Pat. No. 3,743,095 to Mensing et al. proposes the use of a vortexseparator to separate oil from an oil/water mixture which results fromoil spills on a body of water.

Robertson et al., "HYDROCYCLONE FOR THE TREATMENT OF OIL-SPILLEMULSIONS", Paper F3 presented at the Second International Conference onHydrocyclones at Bath, England, Sep. 19-21, 1984, discusses the use ofhydrocyclones for the treatment of oil spill emulsions. It dealsprimarily with the breaking down of the emulsion to remove a portion ofthe water content thereof.

SUMMARY OF THE INVENTION

The present invention provides an oil spill recovery system utilizing anovel combination of a first hydrocyclone separator hydrocyclonefollowed by a second hydrocyclone separator, the combination of whichprovides a highly efficient separation of clean water which can bereturned to the sea thus maximizing the oil concentration in the fluidswhich must be stored on the recovery vessel.

A skimmer or other conventional oil spill recovery means recovers fromthe sea a recovered fluid containing oil and water. This recovered fluidis conducted to a floating vessel floating on the body of water.

A hydrocyclone system located on the floating vessel includes a firsthydrocyclone separator and a second hydrocyclone separator. In the firsthydrocyclone separator, the recovered fluid is separated into a firstunderflow stream containing primarily free water, and a first overflowstream which primarily contains the oil and water emulsion recoveredfrom the sea.

The first underflow stream, containing primarily free water with somefree oil dispersed therein, then may run through the second hydrocycloneseparator which separates that stream into a second underflow streamwhich is clean water which can be returned to the sea, and a secondoverflow stream which contains the remaining oil which was removed fromthe free water.

The first overflow stream containing the oil and water emulsion isdirected to ship's storage where it is held until it is subsequentlyconveyed to an on-shore processing facility. The second overflow streammay also be directed to ship's storage or it may be recycled.

In one embodiment, the system described above takes the recovered fluidfrom the sea and sends it directly to the first hydrocyclone separatorwithout any substantial gravity separation being permitted. In a secondembodiment, the recovered fluid is first directed to ship's prestoragewherein some gravity separation is permitted, and then a water leg fromthe prestorage is pumped to the first hydrocyclone separator.

An alternative embodiment is provided wherein the hydrocyclones aresupported on a remote floating skimmer.

Various monitoring and control systems are disclosed for use with thefirst hydrocyclone separator in order to optimize the efficiency thereofin response to varying flow rates and oil concentrations in therecovered fluid.

Numerous objects, features and advantages of the present invention willbe readily apparent to those skilled in the art upon a reading of thefollowing disclosure when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first embodiment of the oilspill recovery system of the present invention wherein recovered fluidsare sent directly through a static mixer to the first hydrocycloneseparator without any opportunity for substantial gravity separation ofthe oil and water.

FIG. 2 is a schematic illustration of a second embodiment of theinvention wherein the recovered fluids are first directed to ship'sprestorage wherein the oil and water emulsion is allowed to separatesomewhat from the free water, before the recovered fluids are directedto the first hydrocyclone separator.

FIG. 3 is a schematic illustration of a first embodiment of a monitoringand control system for use with the first hydrocyclone separator.

FIG. 4 is a schematic illustration of a second embodiment of amonitoring and control system for the first hydrocyclone separator.

FIG. 5 is a schematic illustration of a third embodiment of a monitoringand control system for the first hydrocyclone separator.

FIG. 6 is a schematic illustration of a fourth embodiment of amonitoring and control system, illustrating the possibility ofmonitoring the underflow from the second hydrocyclone separator.

FIG. 7 is a schematic illustration of a fifth embodiment of a monitoringand control system wherein flow rate control is present in the underflowstream and a split ratio control is present on the overflow stream.

FIG. 8 is a schematic illustration of a system similar to that of FIG.1, except that the hydrocyclones are supported on a remote floatingskimmer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a first embodiment of the oil spill recoverysystem of the present invention is shown and generally designated by thenumeral 10. The recovery system 10 includes a floating vesselschematically illustrated within the phantom line boundary 12 which isfloating on a body of water 14, i.e., the sea 14.

The floating vessel 12 has a storage zone 16 defined therein which iscommonly referred to in this disclosure as ship's storage 16.

The system 10 includes an oil recovery means 18 which may be aconventional skimmer and pump device for recovering from the sea arecovered fluid containing oil and water which is pumped through arecovered fluid supply conduit means 20 on board to the floating vessel12. Spilled fluids could also be recovered onto a conventional skimmership which scoops up the fluid as it moves through the sea.

The nature of the recovered fluids may of course vary widely dependingupon the nature of the fluid which was spilled, and the subsequentevolvement of that fluid over time due to environmental conditions.Typically the recovered fluids will contain a relatively low percentage,e.g., ten percent by volume, of an oil and water emulsion often referredto as a mousse. The remainder of the recovered fluid will be free seawater with some small amount of free oil dispersed therein. The oil andwater emulsion or mousse is typically a very stable emulsion containingthe heavier hydrocarbons which are left after the lighter hydrocarbonsevaporate. Typically the emulsion has been highly agitated by wind, waveand rain action and the water contained in the emulsion is tightly boundtherein. Also the emulsion will often be at relatively low temperaturesand thus be relatively viscous.

With the system 10 of FIG. 1, the recovered fluids are normallyconducted directly to an inlet 22 of a first hydrocyclone separator 24.The preferred geometry for first hydrocyclone separator 24 is furtherdescribed below.

The recovered fluid first flows through a static mixer 26 disposed insupply conduit 20 which provides a means for mixing the oil and water ofthe recovered fluid, for thereby reducing oil slugs which may reach thefirst hydrocyclone separator 24. It will be understood that the fluidrecovered by recovery device 18 will be very non-uniform in its makeupover a period of time. That is, the recovered fluid will from time totime have greatly varying concentrations of oil therein and may in factinclude oil slugs of nearly pure oil from time to time. The firsthydrocyclone separator 24 is designed to handle relatively lowpercentages of oil, and thus its operating efficiency can be improved ifthe oil slugs in the recovered fluid can be somewhat smoothed outthrough use of the static mixer 26.

From the static mixer 26, the recovered fluid goes through aconventional strainer 28 disposed in supply conduit 20 to remove foreignmaterial often times found in oil spills, and then flows through amonitoring device 30 before it reaches the first hydrocyclone separator24.

The recovered fluid supply conduit means 20 may be described as a meansfor conveying the recovered fluid directly from the recovery device 18to the inlet 22 of first hydrocyclone separator 24 without allowing anysignificant gravity induced separation of oil and water in the recoveredfluid prior to the recovered fluid entering the first hydrocycloneseparator 24.

The monitoring device 30 is provided to monitor the makeup of therecovered fluid flowing through the recovered fluid supply conduit means20 toward the first hydrocyclone separator 24. If it is determined thatthe recovered fluid contains an oil concentration in excess of thatwhich can be handled by the first hydrocyclone separator 24, then therecovered fluid is diverted through a bypass conduit 32 to the ship'sstorage 16 without flowing through the hydrocyclone separator system.The control of flow of the recovered fluid to either the firsthydrocyclone separator 24 or through the bypass conduit 32 to ship'sstorage 16 is controlled by first and second control valves 34 and 36which are operably associated with the monitoring device 30 so as to beopen and closed in response to signals received from a control systemcontained therein. If the oil concentration in the recovered fluids isat relatively low levels, the control valve 34 will remain open and thecontrol valve 36 will remain closed, which can be considered theirnormal positions, so that the recovered fluids are directed to the firsthydrocyclone separator 24. If, however, an excessively highconcentration of oil is detected in the recovered fluid by themonitoring device 30, it will cause the control valve 36 to open, andthen cause the valve 34 to close, thus allowing the recovered fluids tobe directed through the bypass conduit 32 directly to ships storage 16.When the oil concentration again drops into its normal range for whichthe first hydrocyclone separator 24 is designed, the valve 34 willreopen and then the valve 36 will reclose thus again allowing therecovered fluids to flow to the first hydrocyclone separator 24. Valve34 optionally could be located in position 34A in second underflowstream 46.

Optionally, the monitoring device could signal underflow control valve34A to close, diverting all recovered fluid through the overflow streams40 and 48 to ship's storage 16, eliminating the need for the bypass line32.

The monitoring device 30 may be an EXAC Model 8300EX mass flow meteravailable from EXAC Corp. of San Jose, Calif., as is further describedin U.S. Pat. Nos. 4,660,421 and 4,711,132, the details of which areincorporated herein by reference. Also other meters operating onprinciples of microwave, light diffraction/absorption, laser energy,density, acoustics, etc., could be used.

The percentage of oil content in the recovered fluids which can behandled by first hydrocyclone separator 24 without need for bypassingthe same through bypass conduit 32 will vary depending upon the degreeof difficulty of separating the oil from the recovered fluids. Forexample, some recovered fluids may be relatively fresh and the emulsionmay not be nearly so tightly bound as in other cases. Typically, themonitoring device 30 would be set so that if greater than fifty percentoil were contained in the incoming recovered fluid stream the entirerecovered fluid stream would be diverted to ships storage. That,however, must be adjusted based upon observations of the performance ofthe hydrocyclone separating system. If the discharged water throughconduit 52 contains excessive amounts of oil, and if this cannot becorrected by modifying the split ratio within the first hydrocycloneseparator 24 itself, then it will be necessary to lower the bypass limiton monitoring device 30 to cause it to bypass the recovered fluids atlower oil percentages.

The first hydrocyclone separator 24 separates the recovered fluid into afirst underflow stream 38 and a first overflow stream 40. Firstunderflow stream 38 may be more generally referred to as a first moredense stream 38, and first overflow stream 40 may be more generallyreferred to as a first less dense stream 40, since underflow stream 38will be more dense than overflow stream 40. The primary purpose of thefirst hydrocyclone separator 24 is to separate most of the bulk freewater from the oil and water emulsion; there may, however, be somerelatively small reduction of the water content of the emulsion itself.The split ratio between the first underflow stream 38 and first overflowstream 40 will generally be controlled and monitored by one of thesystems described in FIGS. 3-7.

The first underflow stream 38 is directed to the inlet 42 of a secondhydrocyclone separator 44. The second hydrocyclone separator 44separates the first underflow stream 38 into a second underflow stream46 and a second overflow stream 48. Again, the second underflow stream46 may be referred to more generally as a second more dense stream, andsecond overflow stream 48 may be referred to as a second less densestream. The second hydrocyclone separator 44, which may be referred toas a de-oiling hydrocyclone, may be constructed in accordance with theteachings of U.S. Pat. No. 4,576,724 to Colman et al., and U.S. Pat. No.4,764,287 to Colman et al., the details of which are incorporated hereinby reference.

A storage conduit means 50 carries the first overflow stream 40 and thesecond overflow stream 48 to the ship's storage 16. Optionally, thesecond overflow 48 may be recycled through recycle conduit 51 ascontrolled by valves 53 and 55.

A water discharge conduit means 52 returns the de-oiling hydrocycloneunderflow stream to the sea 14. A back pressure regulator 54 in conduit52 controls a back pressure on second underflow 46.

A typical example of the flow rates through the various portions of thesystem 10 would be as follows. The incoming flow rate of recovered fluidthrough recovered fluid supply conduit means 20 is designated as Q. Thetypical split ratio in the first hydrocyclone separator 24 would directseventy-five percent Q to the first underflow stream 38 and twenty-fivepercent Q to the first stream 40. All of the oil and water emulsion inthe recovered fluid would be contained in the first overflow stream 40.The first underflow stream 38 would contain primarily free sea waterwith a relatively small amount of free oil dispersed therein and withsome dissolved oil dissolved in the free water. The first underflowstream 38 from first hydrocyclone separator 24 is then de-oiled in thesecond hydrocyclone separator 44 which would split that stream intoapproximately seventy-four percent Q going to the second underflowstream and thus being returned as clean water to the sea, and withapproximately one percent Q being directed to the second overflow streamwhich would return to ship's storage. The one percent Q flowing to thesecond overflow stream 48 would contain most of the free oil which hadpreviously been left in the first underflow stream 38. The secondhydrocyclone separator 44 thus removes most of the free oil from thefirst underflow stream 38, and the second underflow stream 46 willcontain less than 1000 PPM oil, and preferably less than 500 PPM, thusmeeting acceptable limits for water which may be returned to the seaafter an oil spill recovery process. This remaining oil in secondunderflow stream 46 will be in the form of free oil dispersed in freewater and dissolved oil dissolved in free water.

While in certain situations it is conceivable that further oil/waterseparation systems might be disposed downstream of the second underflowstream 46, it is envisioned that in a properly designed system accordingto the present invention the second underflow stream 46 can be returneddirectly to the sea without any need for further cleaning of the water.

It is noted that both the first hydrocyclone separator 24 and the secondhydrocyclone separator 44 may each be comprised of a bank of parallelhydrocyclones. This will be determined based upon the flow rate ofrecovered fluids which must be treated and the design flow rate for theparticular hydrocyclone units which are chosen.

Optionally, a portion of first underflow stream 38 and/or secondunderflow stream 46 may be recycled through recycle conduits 56 and 58as controlled by valves 57 and 59, respectively.

Also in some situations where the first underflow stream 38 is cleanenough to return to the sea, it will be possible to eliminate the secondhydrocyclone separator 44.

The Embodiment of FIG. 8

FIG. 8 illustrates a modification of the system 10 of FIG. 1 which isdesignated as the system 10A.

In the system 10A, the hydrocyclones 24 and 44 and associated piping andvalving are supported from a remote floating skimmer device 18A. Theoverflow streams 40 and 48 are connected by storage conduit 50 to theship's storage 16 located on floating vessel 12.

The Embodiment of FIG. 2

Referring now to FIG. 2, an alternative embodiment of the oil spillrecovery system of the present invention is shown and generallydesignated by the numeral 60. Those components of the system 60 whichare identical to those of the system 10 of FIG. 1 are identified by thesame identifying numerals. The system 60 is modified as compared to thesystem 10 in that the system 60 provides for a prestorage and gravityseparation of the oil and water in the recovered fluids prior tointroducing the recovered fluid to the first hydrocyclone separator 24.

In the system 60, the skimmer device 18 pumps the recovered fluidsthrough a recovered fluid supply conduit 62 to a prestorage zone 64,also referred to herein as ship's prestorage 64, on or within the vessel12. Again, the skimmer device 18 may be remote from the floating vessel12, or the vessel 12 may be a skimmer ship which incorporates its ownskimming device which scoops up fluid as the ship moves through the sea.Prestorage zone may be existing compartmentalized storage in the ship ora storage container on the deck of the ship. If the hydrocyclones aresupported from a remote floating skimmer device as shown in FIG. 8, theprestorage zone 64 could also be located on the remote floating skimmerdevice. The recovered fluid is allowed to reside in the prestorage zonefor a sufficient time to allow significant gravity induced separation ofthe oil and water in the recovered fluid and particularly to allowgravity induced separation of the free water from the oil and wateremulsion which will tend to rise to the top of the prestorage zone 64.

The prestorage zone 64 has a water leg discharge outlet 66 communicatedwith a lower portion of the prestorage zone 64. A suction conduit 68communicates the water leg discharge outlet 66 with a suction inlet of abooster pump 70. A pump discharge conduit 72 connects a discharge outletof the booster pump 70 to the inlet 22 of the first hydrocycloneseparator 24.

Typically, the prestorage zone 64 will be sized so as to provide aresidence time therein on the order of thirty minutes for the recoveredfluids flowing therethrough. In that time, much of the free water willseparate from the recovered fluid and settle toward the lower end of theprestorage zone 64 from which it is withdrawn at the water leg dischargeoutlet 66. Coalescence inducing chemicals may be added in prestoragezone 64, and/or a mechanical coalescing device (not shown) may be placedupstream of first hydrocyclone separator 24.

Much of the oil and water emulsion will separate out in the ship'sprestorage 64 and will pass over a weir 65 and will be drawn off by abooster pump 67 which will pump the skimmed oil and water emulsionthrough an oil line 69 to the ships storage 16. This may also beaccomplished in some cases by gravity flow. Additionally, if excess oilbuilds up in the prestorage 64 and is pulled through the water legdischarge outlet 66 by the booster pump 70, this will be monitored bythe monitoring device 30 which can divert or bypass the fluid throughbypass conduit 32 directly to ship's storage 16 in a manner previouslydescribed with regard to FIG. 1.

With the modified system of FIG. 2, typical flow rates through thevarious components thereof could be as follows. For a flow rate Q ofrecovered fluid withdrawn from water leg discharge outlet 66, the firsthydrocyclone separator 24 would direct ninety percent Q to its underflowstream 38 and ten percent Q to its overflow stream 40. The secondhydrocyclone separator 44 would then direct one percent Q to itsoverflow stream 48, and eighty-nine percent Q to its underflow stream 46which is returned to the sea.

It is desirable to provide a means for controlling the liquid level inthe prestorage zone 64 to avoid running the pump 70 dry. This can beaccomplished by a partial recycling of second underflow stream 46through recycle conduit 71 as controlled by level controller 61 andcontrol valve 63. Optionally, valve 34A can be operated in response tothe fluid level in prestorage 64 thus changing a back pressure againstpump 70. Also, a variable speed control of pump 70 could be controlledin response to the fluid level in prestorage 64.

Control Systems of FIGS. 3-7

Turning now to FIGS. 3-7, several different approaches to monitoring andcontrolling the split ratio between the underflow and overflow of thefirst hydrocyclone separator 24 are schematically illustrated. It willbe understood that any one of these control systems or combinations ormodifications thereof can be utilized with the first hydrocycloneseparator 24 in either the system 10 of FIG. 1, the system 10A of FIG.8, or the system 60 of FIG. 2.

Such a monitoring and control system is generally desirable because ofthe constantly changing water-to-oil ratios expected in the recoveredfluid stream from the skimmer 18. If a situation were encountered wherea relatively constant water-to-oil ratio is present, such as is likelyin the system of FIG. 2, then there would be no need for such amonitoring and control system.

Generally speaking, a makeup of at least one of the incoming recoveredfluid stream 20, the first underflow stream 38, the first overflowstream 40 and the second underflow stream 46 is monitored. The "makeup"of the stream refers to the relative proportions of the oil and water inthe stream.

FIG. 3 illustrates the monitoring of the makeup of the incomingrecovered fluid stream 20. A monitoring means 74 is placed in therecovered fluid stream 20. The monitoring means 74 preferably is a massflow meter of the same type described above for the mass flow meter 30of FIG. 1. It will be understood that the mass flow meter 30 and themetering device 74 may in fact be one single monitoring device used bothto control the split ratio of first hydrocyclone separator 24 and alsoto bypass the entire recovered fluid stream directly to ship's storage16 if the oil concentration thereof is so high that it cannot be handledby the first hydrocyclone separator 24.

Based upon the incoming water-to-oil ratio monitored by the mass flowmeter 74, the position of a control valve 76 is changed by a controlsystem 78 so as to control the split ratio, that is the ratio of thefluid flow rate of the first underflow stream 38 to that of the firstoverflow stream 40. Alternatively or in addition to the control valve 76in the underflow stream 38, there may be a control valve 77 in the firstoverflow stream 40 which may also be utilized to help control the splitratio between the first underflow stream 38 and first overflow stream 40in response to command signals from the control system 78.

The control system 78 associated with the monitoring device 74 andcontrol valve 76 will be constructed so as to control the split ratio asdesired in response to the monitored incoming water-to-oil ratio. Forexample, in many situations it is desirable to have a split ratiobetween the underflow and overflow nearly equal to the water-to-oilratio. That is, if the monitoring device 74 determines that the incomingstream is made up of ninety percent water and ten percent oil, thecontrol system 78 may adjust the control valve 76 so that approximatelythe same ninety percent-ten percent ratio is present between theunderflow stream 38 and the overflow stream 40. Although the theoreticalpreference in some cases may be for the split ratio to be equal to theincoming fluid ratio, in reality an exact separation cannot be achievedand thus the general practical preference is to operate the underflowrate at slightly less than the incoming water percentage thus pushing anexcess of water to the overflow to insure a cleaner underflow at theexpense of wetter oil. Typically the underflow ratio will be somewherein the ratio of fifty to ninety percent of the inlet water percentagedepending on the difficulty of separation. For situations whereseparation is relatively easy, the underflow rate would typically beapproximately ninety percent of the incoming water percentage. Forsituations where separation is difficult, the underflow rate may be aslow as fifty percent of the incoming water percentage. Thus, the splitratio can be said to be proportional to the incoming water percentage.

The control system 78 may also have associated therewith various meansfor monitoring the flow rate through the underflow stream 38 and theoverflow stream 40 to confirm that the desired split ratio has beenachieved. For example, first, second and third pressure monitoring means80, 82 and 84 may be connected to the inlet line 20, overflow line 40,and underflow line 38, respectively. Signals corresponding to the sensedpressure at those locations are communicated back to the control system78 through the various electrical connecting means illustratedtherebetween. It will be understood by those skilled in the art that thepressure drop between 80 and 84 provides a measure of the flow ratethrough the underflow stream 38 whereas the pressure drop between 80 and82 provides a measure of the flow rate through the overflow stream 40for a particular hydrocyclone separator 24.

The control system 78 may be microprocessor based, but it does not haveto be.

FIG. 4 illustrates an alternative control system wherein it is themakeup of the underflow stream 38 that is monitored with a monitoringdevice 86. Due to the much lower oil concentrations present in theunderflow stream 38 as compared to the inlet stream 20, the monitoringdevice 84 may be a turbidity meter. One suitable such monitoring deviceis the Optek Model No. 510E/TF10-ASA-EX available from KC Controls,Ltd., of Reigate, Surrey, United Kingdom. The Optek turbidity meter is asimple optical light absorption monitor which is used to measure thequality of the underflow water stream and thus to use this variable tocontrol the split ratio. Monitoring of the underflow stream 38 issimpler than monitoring of either the inlet stream 20 or overflow stream40 as it deals with relatively low levels of oil in water. Other typesof monitoring devices such as those described above for device 30 couldalso be used.

The turbidity meter 86 provides an indication of the concentration ofoil in the oily water stream 38 as increasing oil content increases thecloudiness or turbidity of the fluid. Again, the monitoring device 86 isconnected to the control system 78 which operates control valves 76 or77. Although not illustrated in FIG. 4, the control system 78 can haveassociated therewith various flow rate indicating measuring devices suchas the pressure monitoring devices 80, 82 and 84.

With the system of FIG. 4 wherein the turbidity meter 86 monitors theoil content of the underflow stream 38, the control system 78controlling control valve 76 will have both an upper limit and a lowerlimit set therein for the oil content of the underflow stream 38. Whenthe oil content of the underflow stream 38 exceeds the upper limit ofcontrol system 78, the control system 78 will act to reduce the openingthrough the control valve 76 thus decreasing a percentage of the inletstream 20 which goes to the underflow stream 38 thereby protecting thequality of the underflow stream 38 and ultimately of the dischargedwater stream 52. On the other hand, if the monitored oil content of theunderflow stream 38 drops below a lower limit set within the controlsystem 78, the control system 78 will cause the opening through controlvalve 76 to be increased thus increasing the percentage of the inletstream 20 which goes to the underflow stream 38 thus reducing the amountof water going into the overflow stream 40 and thus reducing the amountof water which is unnecessarily stored in ship's storage 16.

Typically the first underflow stream 38 from the first hydrocycloneseparator 24 should contain approximately 2,000 PPM oil. Streams of thisquality can then be adequately further de-oiled in second hydrocycloneseparator 44 to provide satisfactory discharge water qualities indischarge stream 52. These desired results could correspond for exampleto high and low limits set in the control system 78 of 10,000 PPM and300 PPM oil, respectively, for the first underflow stream 38.

FIG. 5 illustrates yet another alternative control arrangement in whicha monitoring device 88 is placed in the first overflow stream 40. Themonitoring device 88 is preferably a mass flow meter of the same styleas the mass flow meter 30 described with regard to FIG. 1. Again,monitoring device 88 is connected to the control system 78 whichcontrols control valves 76 and/or 77. Again, the control system 78 mayhave associated therewith various pressure monitoring devices 80, 82 and84.

FIG. 6 schematically illustrates another alternative control system inwhich the quality, that is the degree of oil contamination, in thedischarge clean water stream 46, 52 is directly monitored by monitoringdevice 90. The monitoring device 90 may be a turbidity meter of the sametype as described above in connection with monitoring device 86 of FIG.4. The monitoring device 90 is connected to control system 78 which cancontrol the control valve 77 in the first overflow stream 40 and/or acontrol valve 92 placed in the second underflow stream 46.

FIG. 7 illustrates another control system in which the flow rate throughfirst hydrocyclone separator 24 is controlled either with fixed orificeplate restriction 94 or a back pressure regulator 96. Monitoring devices86 and 74 and control system 78 control the control valve 77 in firstoverflow stream 40 to control the split ratio. If the second separator44 is used, the fixed orifice restriction 94 would preferably be locatedin second underflow stream 46; this would prevent shearing of oildroplets in first underflow stream 38 as it passed through fixed orificerestriction 94.

Of course, a control system for the separation systems shown in FIGS. 1,2 or 8 could utilize multiple monitoring devices monitoring one or moreof the various streams as illustrated in FIGS. 3-7. Also, more than onecontrol valve could be utilized, including any of the examples shown inFIGS. 3-7 or combinations thereof. Depending upon the characteristics ofthe particular system involved, the most appropriate monitoring andcontrol points can be chosen so as to control the split ratio betweenthe first underflow stream 38 and first overflow stream 40 of the firsthydrocyclone separator 24 and thus assure the most efficient operationthereof to provide suitably clean water discharged to the sea throughdischarge conduit 52 while still minimizing any unnecessary diversion ofwater to the ships storage 16.

In some circumstances where the variation of the oil concentration inthe incoming recovered fluid stream is relatively constant, such amonitoring and control system may not be necessary. For example, if theoil concentration of the recovered fluid stream entering the firsthydrocyclone separator 24 can be maintained at no greater than about tenpercent oil and thus ninety percent water, then a first hydrocycloneseparator 24 having a fixed split ratio can be utilized. In such asituation, the first hydrocyclone separator 24 would typically be set tohave a split ratio such that ninety percent of the incoming flow went tothe first underflow stream 38 and ten percent of the incoming flow wentto the first overflow stream 40. This can be accomplished with either afixed orifice plate 94 or a back pressure controller 96 like those shownin FIG. 7.

Preferred Geometry For First Hydroyclone Separator 24

It should be emphasized that the hydrocyclone separator concept asdescribed in this disclosure is defined in terms of the processperformed by the hydrocyclone separator, not by the particular geometryof the hydrocyclone. Nevertheless, preferred geometries are beingdisclosed.

Hydrocyclone separators of the prior art have typically been optimizedfor the purpose either of de-oiling in which a relatively smallpercentage of oil is removed from a water stream, or dewatering in whichthe incoming oil/water stream contains much larger concentrations ofoil.

In the de-oiling hydrocyclones of the prior art exemplified by U.S. Pat.Nos. 4,576,724 and 4,764,287 each to Colman et al., the hydrocyclone isdesigned for a water-continuous phase with a dispersion of oil therein.With the dewatering hydrocyclones exemplified by U.S. Pat. No. 4,749,490to Smyth et al., the incoming oil/water mixture typically contains fromsixty to eighty percent oil and correspondingly from forty to twentypercent water, thus providing an oil continuous phase with waterdroplets dispersed therein.

The preferred first hydrocyclone separator 24 of the present inventionis intended for use in situations where there typically will be a watercontinuous phase and wherein the oil and water mixture will contain atleast sixty percent water by volume, which will insure that it is thewater phase which is continuous. At water concentrations in the range offrom thirty to sixty percent, it is difficult to predict whether thewater or oil will form the continuous phase of the mixture, and a phaseinversion situation can be encountered which is undesirable.

If the oil concentration exceeds sixty percent, then preferably thefluid will be bypassed directly to the ships storage 16 through bypassconduit 32 as seen in FIG. 1.

It has been determined that the preferred geometry for the firsthydrocyclone separator 24 of the present invention, when operating on acontinuous water phase, is that generally similar to the de-oilinghydrocyclone as shown in U.S. Pat. Nos. 4,576,724 and 4,764,287, thedetails of which are incorporated herein by reference, except that thediameter of the overflow outlet should be increased as compared to thepreferred diameters disclosed in the cited patents for the de-oilinghydrocyclones. Where, for example, the preferred de-oiling hydrocyclonegeometry of U.S. Pat. No. 4,576,724 to Colman et al. has a ratio of d₀/d₂ of less that 0.1, the preferred first hydrocyclone separator 24geometry would have d₀ /d₂ greater than 0.1 and typically less then0.35. Preferably no vortex finder is used on the overflow outlet. Ifhigh oil content is encountered it may even be desirable to use d₀ /d₂up to 0.5 with possible inclusion of a vortex finder to prevent shortcircuiting.

As used in U.S. Pat. No. 4,576,724 and herein, d₀ refers to the diameterof the overflow outlet and d₂ is the diameter of the divergent end ofthe intermediate portion of the cyclone chamber.

Thus it is seen that the apparatus and methods of the present inventionreadily achieve the ends and advantages mentioned as well as thoseinherent therein. While certain preferred embodiments of the inventionhave been illustrated and described for purposes of the presentdisclosure, numerous changes in the arrangement and construction of theinvention may be made by those skilled in the art which changes areencompassed within the scope and spirit of the present invention asdefined by the appended claims.

What is claimed is:
 1. An apparatus for recovering oil spilled in a bodyof water comprising:(a) means for recovering a fluid stream containingoil and water from a body of water; (b) monitor means for monitoring themakeup of the recovered fluid stream; (c) a first hydrocyclone means forreceiving and separating the monitored fluid stream into a first moredense stream and a first less dense stream; (d) control means forcontrolling the split ratio between the first more dense stream and thefirst less dense stream in response to only the monitor means; (e)storage means for receiving at least a majority of the first less densestream; (f) a second hydrocyclone means for receiving and separating thefirst more dense stream into a second more dense stream and a secondless dense stream; and (g) means for returning at least a majority ofthe second more dense stream to the body of water.
 2. An oil spillrecovery process for recovering spilled oil from a body of watercomprising the steps of:(a) recovering a fluid stream containing oil andwater from the body of water; (b) monitoring the makeup of the recoveredfluid stream; (c) separating the monitored fluid stream into a firstmore dense stream and a first less dense stream in a first hydrocyclone;(d) controlling the split ratio between the first more dense stream andthe first less dense stream in response to only the monitoring of step(b); (e) storing at least a majority portion of the first less densestream in a storage zone; (f) separating the first more dense streaminto a second more dense stream and a second less dense stream in asecond hydrocyclone; and (g) returning at least a majority portion ofthe second more dense stream to the body of water.